The present invention relates to a transmitter-receiver that includes a transmitter filter and a receiver filter with different center frequencies.
High-frequency wireless devices such as mobile phones generally use different frequencies for transmitting and receiving. In such cases, since the transmitter-receiver uses a single antenna, a duplexer is required. A duplexer essentially includes a transmitter filter and a receiver filter.
A transmitter filter is set up so that signals in the transmission band can pass and signals in the reception band are attenuated to prevent leakage of the signal from the power amp into the reception band. The receiver filter is set up so that it allows signals in the reception band to pass and signals in the transmission band are attenuated to prevent the transmission signals from the power amp from saturating the low-noise amplifier.
However, in mobile phones of recent years, the reception band and the transmission band are close together in frequency. Thus, in order to provide adequate transmission-reception separation, i.e., attenuation of the reception band by the transmitter filter and attenuation of the transmitter band by the receiver filter, measures had to be taken such as making the resonator used in the filter larger to increase the Q value.
Such methods lead to larger duplexers and complex structures, which can lead to increases in the production costs for transmitter-receivers.
It is an object of the present invention to overcome these problems and to provide a transmitter-receiver that can: perform adequate transmission-reception separation using a simple structure; make the transmitter-receiver itself more compact; and simplify the structure and reduce production costs.
A transmitter-receiver according to a first embodiment of the present invention comprises a transmitter including a transmitter element having a transmitter filter and a transmitter antenna connected to the transmitter filter, a receiver including a receiver element having a receiver filter and a receiver antenna connected to the receiver filter, and signal processing means for processing signals transmitted by the transmitter and received by the receiver.
Since each of the transmitter and receiver includes a dedicated antenna, the above-discussed problems with the prior art can be overcome. This allows at least 10 dB of isolation between the transmission band and the reception band. By providing this isolation, the attenuation demands on the filters are reduced, and the transmitter filter and the receiver filter can be made compact. As a result, adequate separation of transmission signals and reception signals can be provided with a simple structure, the transmitter-receiver itself can be made compact, the structure can be simplified, and the production costs can be reduced.
The transmitter and receiver preferably take the form of a subassembly, wherein the transmitter element and the receiver element are both positioned on a substrate, and the transmitter filter and the transmitter antenna are formed integrally in a first monolithic dielectric body, and the receiver filter and the receiver antenna are formed integrally in a second monolithic dielectric body.
More preferably, the transmitter element and the receiver element take the form of a discrete component, wherein the transmitter element and the receiver element are formed integrally in a single monolithic dielectric body.
In each of the above, it is preferred that the filter and antenna of each of the transmitter and receiver elements are formed in separate planar regions of the dielectric body. It is also possible to have the transmitter antenna formed directly above the transmitter filter, separated by a dielectric layer, and to have the receiver antenna formed directly above the receiver filter, separated by a dielectric layer. In this case, the transmitter-receiver itself can be made even more compact.
It is also preferred to provide a shield electrode between the transmitter element and the receiver element. More preferably, a gap is provided between the transmitter element and the receiver element, and a shield electrode is formed at least on an inner perimeter surface of the gap.
It is also possible for the receiver element to include at least two receiver filters and at least two receiver antennae connected to the receiver filters, respectively. In this case, the signal processing means would include a switching mechanism for selecting one of the two receiver filters based on sensitivity.
A transmitter-receiver according to a second embodiment of the present invention comprises a substrate, a transmitter element positioned on the substrate and a receiver element positioned on the substrate. The transmitter element includes a transmitter filter and a transmitter antenna connected to the transmitter filter, the transmitter filter and transmitter antenna being formed integrally in a first monolithic dielectric body. The receiver element includes a receiver filter and a receiver antenna connected to the receiver filter, the receiver filter and receiver antenna being formed integrally in a second monolithic dielectric body.
In a transmitter-receiver according to a third embodiment of the present invention, the transmitter filter is formed on a first transmitter dielectric body, the transmitter antenna is formed on a separate, second transmitter dielectric body, the receiver filter is formed on a first receiver dielectric body, and the receiver antenna is formed on a separate, second receiver dielectric body.
The dielectric material is preferably an inorganic material, because these dielectric materials have high reliability and large dielectric constant, the latter enabling size reduction of both the filter and the antenna. Low resistivity metals, such as Ag and Cu, are preferable as the conductor embedded in the dielectric material to reduce the loss at the filter and the antenna. Such low resistivity conductor materials often have low melting temperatures (e.g., about 950xc2x0 C.), thus making it difficult to co-fire the conductors with conventional ceramic dielectric materials. Accordingly, of the known inorganic dielectric materials, it is most preferred to use dielectric materials which can be fired at low temperature, such as glass materials (e.g., a mixture of cordierite glass, TiO2 powder and Nd2Ti2O7), and ceramic materials obtained by adding a slight amount of glass powder to a dielectric ceramic powder (e.g., barium oxide-titanium oxide-neodymium oxide).
It is also preferred that the spacing between the transmitter antenna and the receiver antenna be at least {fraction (1/16)}xcexave, wherein xcexave is the average wavelength of the transmitter signal and the receiver signal.